Fireplace backer

[PotterD]

For an older Bis woodburning fireplace I have attached 1/4 hardie backer surround. It is loose against the fireplace sheet metal but secured to studs on both sides. While deciding on tiles, a hairline crack developed over the door of the fireplace. I filled with thinset (mapei ultraflex) and fiber tape. Weeks later, I burned a couple logs hot and the crack returned. Should I open the crack and refill? Or tile over the crack? ?? Thanks.

 

[lostinthelight]

Picture?

 

[PotterD]

This extends from directly above the door to the underside of the mantel.

 

[lostinthelight]

Could you take from further out showing the whole stove and fireplace

 

[PotterD]

There is no cracking problem at the joints, just above the door where it has gotten hotter.

 

[lostinthelight]

Can you draw in where the metal studs are are distance between them

 

[PotterD]

There are no metal studs. There are wood studs flanking the fireplace and a header above. You can see where the backer screws are driven in.

 

[lostinthelight]

There are no metal studs. There are wood studs flanking the fireplace and a header above. You can see where the backer screws are driven in.

That seems a large unsupported distance for such thin boarding. I cant see the construction behind but it appears you could be very close to combustibles to comply with regs